A Radio Pulsar Spinning at 716 Hz

TLDR

The pulsar’s very low flux density and roughly 40 % eclipse fraction make it difficult to detect, implying that even faster spinning neutron stars may exist. We discovered a 716‑Hz eclipsing binary radio pulsar in Terzan 5, the fastest known neutron star, which limits its radius to <16 km if its mass is <2 M☉ and challenges r‑mode gravitational‑radiation spin‑down models.

Abstract

We have discovered a 716-hertz eclipsing binary radio pulsar in the globular cluster Terzan 5 using the Green Bank Telescope. It is the fastest spinning neutron star found to date, breaking the 24-year record held by the 642-hertz pulsar B1937+21. The difficulty in detecting this pulsar, because of its very low flux density and high eclipse fraction (approximately 40% of the orbit), suggests that even faster spinning neutron stars exist. If the pulsar has a mass less than twice the mass of the Sun, then its radius must be constrained by the spin rate to be <16 kilometers. The short period of this pulsar also constrains models that suggest that gravitational radiation, through an r-mode (Rossby wave) instability, limits the maximum spin frequency of neutron stars.